This invention relates to mechanisms for closing the throttle flap of an internal combustion engine. Throttle closing mechanisms usually make use of a diaphragm arranged inside a pot-shaped housing. Air flow between the chambers on either side of the diaphragm is restricted by a small opening. When the throttle is released, a plunger connected to the diaphragm prevents rapid closing of the throttle flap, which might cause the engine to stall.
While the slow closing effect provided by the diaphragm is desirable during normal operation of the engine, a rapid closing of the throttle flap is desired when the engine ignition switch is shut off to prevent engine "dieseling" or "run-on". A prior art solution to the run-on problem makes use of a magnetically activated diaphragm by-pass valve which vents the chambers on opposite sides of the diaphragm when the ignition switch is shut off, thereby to effect rapid closing of the throttle flap. When the ignition switch is turned on, an electromagnet closes the by-pass valve thereby effecting normal operation of the throttle closer.
The prior art solution to the run-on problem requires the use of an electromagnetically activated pneumatic valve and tubes connecting the closer chambers to the valve. In addition to the added expense of the pneumatic valve and tubes, this prior art mechanism is subject to malfunctioning, particularly after long use in the environment of an internal combustion engine. The by-pass valve and connecting tubes may become inoperative due to the accumulation of dirt. In this case, leaks will develop so that the throttle closing mechanism is ineffective not only when the ignition is turned off, as is desired, but also when the ignition is on, as is undesired.
It is therefore an object of the present invention to provide a new and improved throttle closing mechanism which effectuates complete closing of the throttle flap when the ignition is turned off.
It is a further object of the invention to provide such a mechanism with simple and low-cost construction.
It is a still further object of the invention to provide such a mechanism which is not subject to wearing out after long use in the environment of an internal combustion engine.